1. Field of the Invention
The present invention relates to a method of, and apparatus for, the continuous dimensional calculation and flaw analysis of manufactured tubular products in a non-contacting manner over a wide range of temperatures (0.degree. F. to 3000.degree. F.) by means of penetrating and computer-processed modeling algorithms.
2. Description of the Prior Art
In the manufacture of tubular products, such as seamless, extruded, stretched or welded pipe, it is important to measure the dimensions of the tube during its manufacture on a continuous basis at elevated temperatures to reject tube which fails to meet specifications and to provide information so that production errors can be promptly corrected to assure proper specifications of the final product. The more quickly the dimensional analysis can be made, the less tube produced will be out of specification, producing cost savings to the manufacturer. It is also desirable, when measuring the dimensions of the tube, that the measuring device be non-contacting with the tube, and that the measuring device be capable of producing continuous measurements, since the production of many tubular products is performed on a continuous basis.
In addition to dimensional analysis of manufactured tube, it is desirable to detect any flaws in the tubes that could lead to catastrophic failure once they are placed in use. Tubular products used in applications of high economic risk, such as power plants, aircraft, submarines, oil well casing and drill stems, require close scrutinization for flaws because failure of such products can result in costly losses of time, equipment, and possibly, personnel.
In the past, penetrating radiation systems have been used for non-contacting, non-destructive measurement of industrial products. In general, the radiation inspection techniques currently used involve the use of an x-ray or gamma ray source situated on one side of the tube to be inspected with a radiation detector located on the opposite side of the tube. The level of radiation intensity detected through the tube can be directly correlated to the average wall thickness of the tube. Such a system is illustrated in U.S. Pat. No. 2,462,088.
Various improvements have been made in the radioactivity inspection systems that produce more accurate and varied information regarding tube dimensions. By increasing the number of source-detector pairs, measurements of individual wall thickness and eccentricity can be obtained. Such systems are exemplified by U.S. Pat. Nos. 3,109,095 and 4,393,305. In U.S. Pat. No. 4,393,305 at least three source-detector pairs are arranged about the tube to be measured so that two of the radiation beams pass through each of three points to be measured on the tube. The measured values of radiation intensities detected can then be processed, using, for example, the method of least squares, as more specifically described in U.S. Pat. No. 4,393,305, to yield measurements of the inside diameter and the outside diameter (and, naturally, wall thickness) at the three points measured, as well as to indicate the eccentricity of the tube.
All of the radiation apparatus that have been previously developed to measure tube dimensions have the limitation of producing measurements at only a limited number of separate points about selected cross sections of the tube. The number of points that can be measured has been limited by the number of source-detector pairs that can be physically situated about the tube. Thus, previous tube examination systems have not provided measurement information for an entire cross section of tube. Further, the previous systems required that the tube be closely constrained to a particular position. Constraints added mechanical complexity, cost, and a significant source of measurement error. The constraining forces may also damage the product or slow the inspection process.
Previous tube examination apparatus can measure numerous points at a given cross section by rotating the source-detector pair relative to the tube and taking several sets of radiation intensity measurements. Such a system is exemplified in U.S. Pat. No. 4,187,425. However, the disclosed apparatus cannot provide complete cross sectional measurement information for a tube that is being continuously produced. Instead, such rotating systems produce measurements only along a helical path about the pipe when such systems are used in continuous production applications.
Recent developments have been made in the areas of Computed Tomography (CT), primarily in medical applications, that provide apparatus and methods for the examination of entire cross sections of objects. Theories used in this technology have application in the measurement and examination of industrial objects. Specific discussions of apparatus and methods for employing CT principles can be found in U.S. Pat. Nos. 4,284,895 and 4,437,006.
CT examination techniques provide advantages over previous pipe examination techniques in that they can be adapted to examine the complete cross section of the tube. Previous CT scanning apparatus such as those disclosed in U.S. Pat. Nos. 4,284,895 and 4,437,006, however, required that (1) the object to be examined be held stationary during the scans, and (2) in order to obtain accurate information regarding the cross section of the object, at least several hundred measurements needed to be taken by rotating the source-detector pair relative to the object.
Although the x-ray and gamma ray sources and detectors disclosed in these previous patents relating to CT scanning apparatus demonstrated the principles for rapid examination of cross sections of objects, such sources and detectors are not suitable for the rapid examination of cross sections of very opaque objects, such as many tubular products formed from steel. Changes in the sources in an effort to adapt such CT systems for denser objects may, in turn, render the previous detector systems unsuitable for such sources because improved pulse height discrimination is required, which necessitates an improvement in previous electronic discrimination techniques. Lastly, in order to rapidly obtain high precision dimensional measurements of roughly regular geometries without the necessity of several hundred sets of scans as is common in conventional tomographic reconstruction, a model had to be developed which could use data from fewer angle scans to generate the required high-precision dimensional measurements. In summary, the above-described limitations render previous CT examining apparatus less suitable for examining continuously produced objects such as seamless, extruded, stretched or welded tube for the purpose of making high-precision measurements of and detecting flaws in such tubular products.